07. Piston Engine Power Augmentation

Question 1

Normal aspirated engine

The charge mass that can enter the cylinder is dependant on what 2 things regarding air within the inlet manifold

Answer 1

1. DENSITY
2. PRESSURE

Pg 165

Question 2

Density varies with which 3 things

Answer 2

1. Temperature
2. Altitude
3. Humidity

Pg 166

Question 3

Density varies with ____, ____, and ____, so the best means to determine engine power is by what

Answer 3

1. TEMPERATURE
2. ALTITUDE
3. HUMIDTY
4. DENSITY ALTITUDE

DA = PA + ((Actual Temp - ISA temp) x 118)

Pg 166

Question 4

What is the density altitude formula

Answer 4

Density altitude = Pressure altitude + (Diff. between actual & ISA Temp x 118)

DA = PA + ((Actual - ISA) x 118)

EXAMPLE:
An aircraft plans to take off from an airfield at an altitude of 4000ft.
The OAT is 21℃.
The ISA temp for 4000 ft should be 7℃
ISA temp = 15 - (alt x 2) ⋉ 15 - (4 x 2) ⋉ 15 - 8 = 7℃
21 - 7 = 14
4000 + (14 x 118) ⋉ 4000 + 1652 = 5,652 ft
This means the max power produced by the engine at this airfield on this day is equivilant to an engine operating at almost 5,700 ft

Pg 166

Question 5

Engines produce the most power when they are HOT & HIGH or when they are LOW & COLD

Answer 5

LOW and COLD

Idea would be winter sea level conditions when air is cold, dry, and dense

Pg 166

Question 6

Complete the following graph that shows a Normally Aspirated Engine Performance
LINK HERE

Answer 6

1. Performance available - Sea Level
2. Performance available - Altitude
3. TAS
4. Power

LINK HERE

Pg 167

Question 7

Piston Engine Power & Performance

When considering power output, the efficiency of which component of the engine must be taken into account

Answer 7

PROPELLER

Pg 167

Question 8

At high atmospheric densities, the engine produces more power and needs MORE or LESS power to turn the propeller

Answer 8

MORE

Pg 167

Question 9

Propeller efficiency varies significantly with ____ as well as density

Answer 9

AIRSPEED

Pg 167

Question 10

What are the 3 operational descriptions of power output

Answer 10

1. Take-off
2. Rated
3. Cruise

1. Take-off - is the max power the engine can produce
2. Rated - Power available under specific conditions
3. Cruise - Expressed normally as a percentage of max power

Pg 168

Question 11

Normally aspirated engines mass of charge entering the cylinder will INCREASE or DECREASE with increasing density altitude

Answer 11

DECREASE

Read “increasing density altitude” as increase in altitude and not as density increasing.
Density increasing means thicker, denser air, where as altitude increasing means a decreasing density.
Remember - Density Altitude is just a point in the sky (altitude) at which the aircraft is at

Pg 169

Question 12

By ____ ft, a normally aspirated engine will have lost ____% of its power

Answer 12

1. 20,000 ft
2. 50%

Pg 169

Question 13

Supercharging

What type of system helps maintain normal power output during the climb

Answer 13

COMPRESSOR SYSTEM

Altitude boosted supercharger

Pg 169

Question 14

Supercharging

A compressor system that helps maintain normal power output during the climb is known as what

Answer 14

ATLTITUDE BOOSTED SUPERCHARGER

Pg 169

Question 15

What are the 2 types of supercharging devices

Answer 15

1. Supercharger
2. Turbocharger

Pg 169

Question 16

A superchargers compressor is driven by what

Answer 16

BELT from the CRANKSHAFT

Pg 169

Question 17

A turbochargers compressor is driven by what

Answer 17

EXHAUST GAS

Pg 169

Question 18

What does MAP stand for

Answer 18

MANIFOLD ABSOLUTE PRESSURE
(MAP)

MAP guage is a gauge that measures the manifold absolute pressure

Pg 170

Question 19

What does a MAP GAUGE measure

Answer 19

AIR PRESSURE in INLET MANIFOLD

Gauge measures the pressure of the air being supplied by turbocharger into the inlet manifold

Pg 170

Question 20

What is the difference in terms of measurements between a boost gauge and a manifold absolute pressure gauge (MAP)

Answer 20

BOOST - measures pressure relative to standard sea level
BOOST - can be negative or positive
MAP - pressure displayed as an absolute pressure

Pg 170

Question 21

If the MAP and boost gauges indicate atmosopheric pressure whens stopped on the ground, what is this known as

Answer 21

STATIC BOOST

Pg 170

Question 22

Static boost is a term used to describe what

Answer 22

Engine stopped on the ground
MAP and BOOST gauges indicate atmospheric pressure

Pg 170

Question 23

What does a turbocharger unit comprise of

Answer 23

TURBINE linked to IMPELLER

Pg 172

Question 24

What drives the turbine in a turbocharger engine

Answer 24

EXHAUST GAS

Exhaust gas drives the turbine, which then drives the impeller

Pg 172

Question 25

How does an *impeller* in a *turbocharger* engine impart energy to the air.

Answer 25

ACCELERATES AIR to CIRCUMFERENCE ## Footnote Pg 172

Question 26

*Impeller vanes* are designed to CONVERGE or DIVERGE air

Answer 26

DIVERGE ## Footnote Pg 173

Question 27

As air diverges to the impeller circumference, the air increases in what 3 things

Answer 27

1. Velocity 2. Pressure 3. Temperature ## Footnote Pg 173

Question 28

What is the name of the component which trades velocity for a further increase in pressure and temperature in a *turbochargerd* engine

Answer 28

DIFFUSER ## Footnote Pg 173

Question 29

How does a *diffuser* function in a *turbocharger* engine

Answer 29

Trades VELOCITY for increase in PRESSURE & TEMPERATURE ## Footnote Usually formed by an expanding duct Pg 173

Question 30

Some *turbochargers* use what to cool air before entering the cylinder

Answer 30

INTERCOOLERS ## Footnote Pg 173

Question 31

What are 2 key *advantages* of a *turbocharger*

Answer 31

1. NO ENGINE POWER 2. RPM BOOST ## Footnote Engine Power - No power is taken from the engine to drive the turbocharger As RPM increases, velocity of exhaust gas increases, which increases the impeller speed, thus icnreasing the amount of boost Pg 173

Question 32

What is 1 key *disadvantage* of a *turbocharger*

Answer 32

SPOOL TIME | Turbo lag ## Footnote Turbine is driven by exhaust gases. When RPM increased, it takes a finite amount of time to spool up the turbocharger Pg 173

Question 33

What is *turbo lag*

Answer 33

LAG in BOOST DELIVERED ## Footnote Turbine is driven by exhaust gases. When RPM increased, it takes a finite amount of time to spool up the turbocharger Pg 173

Question 34

If the amount of exhaust gas output is not controlled to drive the turbine, what can this lead to

Answer 34

OVER BOOSTING ## Footnote Excessive mass of charge is pumped into the cylinders Pg 175

Question 35

A sophisticated method of *boost control* is what

Answer 35

WASTE GATE SYSTEM ## Footnote Pg 176

Question 36

What happens to the exhaust gases when the waste gate system is *open* and when it is *closed*

Answer 36

OPEN - Exhaust gases go to atmosphere CLOSED - Exhaust gases to go turbine ## Footnote Pg 176

Question 37

The waste gate system is fitted *PARALLEL* or *IN SERIES* to the turbocharger. The waste gate system is fitted *UPSTREAM* or *DOWNSTREAM* to the turbocharger

Answer 37

1. PARALLEL 2. UPSTREAM ## Footnote Pg 176

Question 38

What is the name of the component that constantly controls and maintains the right amount of boost to the turbocharger

Answer 38

WASTE GATE CONTROLLER ## Footnote Pg 177

Question 39

What does the *waste gate controller* do

Answer 39

MAINTAINS and CONTROLS BOOST ## Footnote Maintains the right amount of boost across a range of ambient conditions Pg 177

Question 40

As altitude *increases* and air density *decreases*, the waste gate controller will OPEN or CLOSE

Answer 40

CLOSE ## Footnote Closes to try and maintain the optimum level of boost delivered to the cylinders Pg 177

Question 41

What is the term given to the point where the *waste gate controller* has completely closed

Answer 41

CRITICAL ALTITUDE ## Footnote Pg 177

Question 42

At *critical altitude* what will happen to MAP pressure and engine power

Answer 42

REDUCES ## Footnote Pg 177

Question 43

On a *supercharger* engine, the equivilant of critical altitude is known as what

Answer 43

FULL THROTTLE HEIGHT ## Footnote Pg 177

Question 44

What is a disadvantage of reaching critical altitude in terms of exhaust gases

Answer 44

BACK PRESSURE VOLUMETRIC EFFICIENCY | Volumetric efficienty in the cylinder due to back pressure ## Footnote All exhaust gas is directed towards the turbine, which causes back pressure THis means some exhaust lags, this remaining in the cylinder, reducing the volumetric efficiency Pg 177

Question 45

What is the *waste gate* position for each of the following stages of flight, and any other significant considerations; 1. Engine start 2. Idle Power 3. Take off 4. Climb 5. Critical Altitude 6. Above critical altitude

Answer 45

1. HELD OPEN - spring pressure 2. FULLY CLOSED - MAP pressure low as little exhaust gas 3. PARTIALLY OPEN 4. CLOSED - Turbine RPM increases 5. FULLY CLOSED - Turbine at max speed 6. FULLY CLOSED - Max value of MAP reduces ## Footnote Pg 178

Question 46

In a *supercharger system* how does the intercooler cool the air entering the engine

Answer 46

COLD RAM AIR | Ducted from atmosphere and passed over induction manifold ## Footnote Pg 179

Question 47

What is *rated power*

Answer 47

MAX POWER at which engine can be operated CONTINUOUSLY ## Footnote Pg 180

Question 48

What is *rated boost*

Answer 48

MANIFOLD PRESSURE allowed for RATED POWER ## Footnote Pg 180

Question 49

# Supercharger If an aircraft climbs at rated boost to the full throttle height, it is said to have reached what

Answer 49

RATED ALTITUDE ## Footnote Rated altitude is the maximum altitude at which maximum continous power can be maintained on a supercharged engine Pg 180

Question 50

What is a supercharged engine at significant risk from with rapid throttle movements

Answer 50

THERMAL SHOCK ## Footnote Pg 180